Project Summary Factors controlling cell shape are crucial to cellular function. This is especially so in neurons, which need to extend axons over long distances in order to connect with their appropriate synaptic partners. Eph receptor tyrosine kinases (EphRs) and their cognate ephrin ligands play key roles in many aspects of nervous system development and are particularly important for axon targeting. How EphRs and ephrins govern the final shape of a neuron and its subsequent synaptic connections is not well understood. We propose to investigate this using the nematode C. elegans as a tractable model for these studies. The C. elegans genome contains only a single EphA receptor and four ephrin-A genes, which greatly simplifies analysis of EphR/ephrin function. Also, the entire nervous system architecture has been determined, allowing one to make predictions of neuron function in response to changes in cell shape. Non-invasive optogenetic tools have been developed that allow the physiological stimulation of single neurons. Similarly, Ca2+-sensitive GFP and RFP variants have been developed allowing one to record changes in Ca2+ dynamics in response to stimuli. Finally, C. elegans exhibits specific behaviors, allowing us to understanding the consequences of cell shape change or physiology at the behavioral level. We recently identified novel roles for the C. elegans EphR gene vab-1, and it's ephrin ligand, efn-4 in controlling AIY interneuron shape. These cells function as a left-right pair and are required for the transduction of thermosensory information. Electron microscopy reveals that the AIYL and AIYR cells make a gap junction contact in the dorsal side of the nerve ring. Our fluorescence reporter data also reveals physical contact between AIYL and R on the ventral side of the nerve ring. Whether these contact points are required for normal AIY function is not known. We propose a genetic approach to assaying the role of AIY morphology in their physiology and behavior. efn-4 mutations cause defects in axon outgrowth, preventing the AIY cells from making dorsal contact. Conversely, efn-1 mutations prevent the AIY cells from making contact on the ventral side of the nerve ring. We hypothesize that AIYL/R communication will be blocked in one or more ephrin mutants. This also suggests that AIY-based behaviors such as isothermal movement will be compromised. This has important implications for predicting and modeling neural circuit function. Our approach will be broadly applicable to investigating the molecular, cellular and behavioral consequences of other genes involved in neural development. The strong conservation of neural function between C. elegans and humans indicates that information gained from a simple model system will have direct influence on the understanding of human neurodevelopmental disorders. This project directly addresses fundamental mechanisms in developmental neurobiology, and will accomplish both broad and specific AREA program goals, including enhancing Kennesaw State University's research environment and exposing students to high quality research through direct participation.